The grimmest prognosis in the draft report is in the details of the effort it would take to actually limit warming to 1.5°C. Countries won’t just have to give up fossil fuels and stop emitting greenhouse gases; they’ll have to pull carbon dioxide straight out of the air. “All pathways that limit global warming to 1.5°C with limited or no overshoot project the use of carbon dioxide removal (CDR),” according to the report. And not just a little, but a lot, upward of 1,000 gigatons of carbon dioxide removed from the atmosphere by the end of the century. This will require machines that scrub carbon dioxide out of the air as well as biofuels coupled with carbon capture and sequestration. These tactics have their own energy demands and environmental drawbacks, and we may not be able to deploy them in time. “CDR deployment of several hundreds of [gigatons of CO2] is subject to multiple feasibility and sustainability constraints,” according to the IPCC report.